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(rice), a genus of annual and perennial plants of the family Gramineae. There are 19 species of rice, growing in the tropics. The cultivated species, Oryza sativa, is divided into the subspecies Oryza s. brevis and Oryza s. communis. The plant is distributed in the subtropics and in the warmest regions of the temperate zone. The species O. glaberrima is cultivated in western Africa. The other 17 species are wild and reproduce by self-seeding. A number of species that grow in Africa, such as O. punctata and O. breviligulata, are widely used as food by the local population.
O. sativa is an annual plant. Its fibrous root system is 30–40 cm in length (up to 1 m) and is distinguished from the roots of other cereal grains by the presence of air-bearing cavities and a small number of hairs. With constant flooding, the hairs almost completely die off in the adult plant. The culm is a straw ranging in length from 50 cm to 5 m (in deep-water forms). The rice plant usually forms three to five productive culms; with sparse planting and abundant feeding, 50 or more such culms develop. The culms of lodge-resistant varieties are very sturdy. The leaf consists of a sheath and a violet, reddish, or green linear-lanceolate blade. The inflorescence is a panicle measuring 10–30 cm long. One-flowered spikelets are borne by short pedicels. The flower consists of two broad red, yellow, or brown flowering glumes, two lodicules, a one-seeded ovary, and six stamens. In some forms, the flowering glumes have an awn. The fruit—a tunicate grain—is rounded and broad in Oryza s. communis and long and narrow in Oryza s. brevis. Inside it is vitreous, semi-vitreous, or mealy. One thousand grains weigh 26–45 g.
O. sativa is a spring plant having a vegetative period from 90 to 165 days. The rice plant requires warm temperatures. The seeds sprout at a soil temperature of 10°–12°C, and the optimum temperature for growth and development is 22°-27°C. Rice is cultivated in irrigated areas or in areas with a great deal of precipitation (1,800–2,000 mm annually). Water requirements vary with different phases of growth. For seed sprouting the upper layer of soil is kept wet. During tillering, shooting, and tasseling, water depths of 5–25 cm are maintained. The water is drained from the paddies during the period of wax ripeness. Rice plants sprout in chernozem, chestnut, marshy, and other soils with slight water permeability. Floodplain soils are particularly favorable.
Rice is the principal cereal crop of the greater portion of the world’s population. Various foods prepared from its grains serve as a substitute for bread among many peoples. The rice grain is processed into alcohol, starch, and beer. The straw is used in the manufacture of valuable types of paper, string, hats, mats, and other items. The bran is fed to animals; it also yields a high-quality oil.
Rice is one of the most ancient crops. Its place of origin has not as yet been established. However, N. I. Vavilov and other scientists have maintained that rice cultivation began in India several millennia ago. This opinion is supported by the presence of many wild Oryza species and intermediate forms in India. The most ancient center for rice cultivation was China, where the crop was raised as early as the fifth millennium B.C. In Africa rice was first cultivated in 2000 B.C., and in Europe in the eighth century A.D. (on the Iberian Peninsula). Rice was known to Europeans considerably earlier, however. The crop was introduced to the New World in the 15th or 16th century. Its cultivation in what is now the United States began in the 17th century. Rice growing appeared in what is now the USSR (Transcaucasia and Middle Asia) in the second and third centuries B.C. Rice became a commercial crop in Australia in the 20th century.
On a worldwide basis, the area under rice cultivation totaled 102.6 million hectares (ha) between 1948 and 1952, 123.5 million ha between 1961 and 1965, 134.6 million ha in 1970, and 134 million ha in 1973. The world’s principal rice producers are the countries of Asia, where more than 90 percent of the world’s plantings are located. Rice occupies more than 36 million ha in India and more than 33 million ha in China. In 1973 rice occupied 0.7 million ha in the United States and about 0.5 million ha in Europe. The gross world harvest was 321.3 million tons, with an average yield of 24 quintals per ha. The highest yields were obtained in Australia and Spain, reaching as much as 70 quintals per ha. The average yield was greater than 50 quintals per ha in Japan, Greece, the Arab Republic of Egypt, and the United States. The yield was considerably less in India, reaching only 16–18 quintals per ha.
In the USSR rice plantings occupied 95,000 ha in 1960, 217,000 ha in 1965, 350,000 ha in 1970, and 462,000 ha in 1973. In 1973 the gross harvest was 1.76 million tons. The average yield was 38.2 quintals per ha (on advanced farms, 60–65 quintals per ha). The average yield was 42.5 quintals per ha in Tad-zhikistan and 40.1 quintals per ha in Kazakhstan.
The best rice varieties are Krasnodarskii 424, Dubovskii 129, Kuban’ 3, Donskoi 163, Primorskii 10, UzROS 263, and Uz-bekskii 5. In 1974, 89 varieties were regionalized. The general direction of selective breeding in the USSR is toward the development of highly productive (a yield of no less than 80–90 quintals per ha), early-ripening, low-growing varieties that possess group resistance to disease and pests and whose grain has technological qualities corresponding to world standards.
Rice is grown in irrigation-ditch systems; crop rotation is practiced. Before sowing, mineral fertilizers are applied: 60–150 kg/ha N, 90 kg/ha P205, and 60 kg/ha K20. Rice is usually sown in rows at a rate of 5.5–7 million viable seeds per ha. The seeds are sown to a depth of 1.5–2 cm. In some countries, including India and China, the seedlings are transplanted. In tending the crop, attention is concentrated on maintaining the proper watering regime, eliminating weeds with herbicides (group 2.4–D) and algae with a 10-percent solution of copper sulfate, and observing a fertilization regime. The rice is harvested by hand or by direct combine. For combine harvesting, the rice is treated first with desiccants.
The most common insects attacking rice are the Ironididae, Lema sovorovi, Hydrellia griseola, Ephydra macellaria, and Thysanoptera. Common diseases include piriculariasis, helmin-thosporium blight, and nematode diseases.
REFERENCESGrist, D. Ris. Moscow, 1959. (Translated from English.)
Erygin, P. S. Fiziologicheskie osnovy orosheniia risa. Moscow-Leningrad, 1950.
Dao Tkhe Tuan. Proiskhozhdenie, sistematika i ekologiia risa. Tashkent, 1960.
Aleshin, E. P., and A. P. Smetanin. Mineral’noe pitanie risa. [Krasnodar] 1965.
Teoriia i praktika vyrashchivaniia risa. Moscow, 1965. (Translated from English.)
Ris. Edited by P. S. Erygin and N. B. Natal’in. Moscow, 1968.
Roesch, M. J. The World of Rice. New York, 1967.
G. A. POMANENKO and E. P. ALESHIN